could not run legacy post zone sub request against new zone products: failed to update user subscription: failed to apply object products: You cannot add or modify subscriptions or services until the outstanding balance is paid. You should be able to do so in your Billing page.
Sorry for the issues, the Support team will need to assist you on a ticket. Can you create a Billing ticket and share your ticket number here? You can open a Billing ticket here, https://dash.cloudflare.com/?to=/:account/support